U.S. patent application number 14/379564 was filed with the patent office on 2015-01-15 for strengthened glass.
The applicant listed for this patent is Nippon Electric Glass Co. Ltd.. Invention is credited to Kosuke Kawamoto, Masato Muguruma, Takashi Murata, Takako Tojyo.
Application Number | 20150017412 14/379564 |
Document ID | / |
Family ID | 49005692 |
Filed Date | 2015-01-15 |
United States Patent
Application |
20150017412 |
Kind Code |
A1 |
Murata; Takashi ; et
al. |
January 15, 2015 |
STRENGTHENED GLASS
Abstract
A tempered glass according to one embodiment of the present
invention is a tempered glass having a compression stress layer in
a surface thereof, the tempered glass including as a glass
composition, in terms of mass %, 45 to 75% of SiO.sub.2, 10 to 25%
of Al.sub.2O.sub.3, 0 to 10% of B.sub.2O.sub.2, 0 to 8% of MgO, 0
to 20% of SrO+BaO, and 0 to 14% of Na.sub.2O. Herein, the term
"SrO+BaO" refers to the total amount of SrO and BaO.
Inventors: |
Murata; Takashi; (Shiga,
JP) ; Tojyo; Takako; (Shiga, JP) ; Muguruma;
Masato; (Shiga, JP) ; Kawamoto; Kosuke;
(Shiga, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nippon Electric Glass Co. Ltd. |
Shiga |
|
JP |
|
|
Family ID: |
49005692 |
Appl. No.: |
14/379564 |
Filed: |
February 19, 2013 |
PCT Filed: |
February 19, 2013 |
PCT NO: |
PCT/JP2013/053941 |
371 Date: |
August 19, 2014 |
Current U.S.
Class: |
428/220 ;
428/410; 501/66; 501/69; 65/114; 65/30.14; 65/99.2 |
Current CPC
Class: |
C03B 27/012 20130101;
C03C 3/093 20130101; H01L 31/0352 20130101; C03C 3/087 20130101;
Y10T 428/315 20150115; C03C 21/002 20130101; G06F 3/01 20130101;
C03B 18/02 20130101; Y02E 10/542 20130101; Y02E 10/541 20130101;
H01L 31/0392 20130101 |
Class at
Publication: |
428/220 ;
65/99.2; 65/114; 65/30.14; 428/410; 501/66; 501/69 |
International
Class: |
C03C 3/093 20060101
C03C003/093; C03B 27/012 20060101 C03B027/012; H01L 31/0352
20060101 H01L031/0352; G06F 3/01 20060101 G06F003/01; C03C 3/087
20060101 C03C003/087; C03B 18/02 20060101 C03B018/02; C03C 21/00
20060101 C03C021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 20, 2012 |
JP |
2012-033749 |
Claims
1. A tempered glass having a compression stress layer in a surface
thereof, the tempered glass comprising as a glass composition, in
terms of mass %, 45 to 75% of SiO.sub.2, 10 to 25% of
Al.sub.2O.sub.3, 0 to 10% of B.sub.2O.sub.3, 0 to 8% of MgO, 0 to
20% of SrO+BaO, and 0 to 14% of Na.sub.2O.
2. A tempered glass having a compression stress layer in a surface
thereof, the tempered glass comprising as a glass composition, in
terms of mass %, 45 to 75% of SiO.sub.2, 10 to 25% of
Al.sub.2O.sub.3, 0 to 10% of B.sub.2O.sub.3, 0 to 4% of MgO, 0 to
20% of SrO+BaO, and 0 to 10% of Na.sub.2O.
3. A tempered glass having a compression stress layer in a surface
thereof, the tempered glass comprising as a glass composition, in
terms of mass %, 45 to 63% of SiO.sub.2, 10 to 25% of
Al.sub.2O.sub.3, 0 to 10% of B.sub.2O.sub.3, 0 to 4% of MgO, 0.1 to
20% of SrO+BaO, and 0.1 to 10% of Na.sub.2O.
4. A tempered glass having a compression stress layer in a surface
thereof, the tempered glass comprising as a glass composition, in
terms of mass %, 45 to 63% of SiO.sub.2, 10 to 25% of
Al.sub.2O.sub.3, 0 to 10% of B.sub.2O.sub.3, 0 to 4% of MgO, 0.1 to
20% of SrO+BaO, and 1 to 10% of Na.sub.2O and having a mass ratio
(MgO+CaO)/(SrO+BaO) of from 0.1 to 1.5.
5. A tempered glass having a compression stress layer in a surface
thereof, the tempered glass comprising as a glass composition, in
terms of mass %, 45 to 63% of SiO.sub.2, 10 to 25% of
Al.sub.2O.sub.3, 0 to 10% of B.sub.2O.sub.3, 0 to 3% of MgO, 0.1 to
15% of CaO, 0.1 to 13% of SrO, 0.1 to 20% of SrO+BaO, and 1 to 8%
of Na.sub.2O and having a mass ratio (MgO+CaO)/(SrO+BaO) of from
0.1 to 1.0.
6. A tempered glass having a compression stress layer in a surface
thereof, the tempered glass comprising as a glass composition, in
terms of mass %, 45 to 63% of SiO.sub.2, 10 to 25% of
Al.sub.2O.sub.3, 0 to 10% of B.sub.2O.sub.3, O to less than 2% of
MgO, 2 to 15% of CaO, 5 to 13% of SrO, 0.1 to 8% of BaO, 5.1 to 20%
of SrO+BaO, and 1 to 8% of Na.sub.2O and having a mass ratio
(MgO+CaO)/(SrO+BaO) of from 0.1 to 0.8.
7. A tempered glass having a compression stress layer in a surface
thereof, the tempered glass comprising as a glass composition, in
terms of mass %, 45 to 63% of SiO.sub.2, 12 to 25% of
Al.sub.2O.sub.3, 0 to 10% of B.sub.2O.sub.3, O to less than 2% of
MgO, 2 to 15% of CaO, 8 to 13% of SrO, 2 to 8% of BaO, 10 to 20% of
SrO+BaO, and 1 to 8% of Na.sub.2O and having a mass ratio
(MgO+CaO)/(SrO+BaO) of from 0.1 to 0.5.
8. The tempered glass according to any one of claims 1 to 7,
wherein a compression stress value of the compression stress layer
is 300 MPa or more, and a thickness of the compression stress layer
is 5 .mu.m or more.
9. The tempered glass according to any one of claims 1 to 7,
wherein the tempered glass has an internal tensile stress of 50 MPa
or less.
10. (canceled)
11. The tempered glass according to claim 1, wherein the tempered
glass has a strain point of 550.degree. C. or more.
12. The tempered glass according to claim 1, wherein the tempered
glass has a temperature at a viscosity at high temperature of
10.sup.2.5 dPas of 1,550.degree. C. or less.
13. The tempered glass according to claim 1, wherein the tempered
glass has a liquidus temperature of 1,200.degree. C. or less.
14. The tempered glass according to claim 1, wherein the tempered
glass has a liquidus viscosity of 10.sup.3.0 dPas or more.
15. The tempered glass according to claim 1, wherein the tempered
glass is used for a substrate for a solar cell.
16. The tempered glass according to claim 15, wherein the tempered
glass is used for a substrate for a thin-film compound solar
cell.
17. The tempered glass according to claim 1, wherein the tempered
glass is used for a substrate for a display.
18. The tempered glass according to claim 1, wherein the tempered
glass is formed into a flat sheet shape by a float method.
19. The tempered glass according to claim 1, wherein the tempered
glass is manufactured by being cooled at an average cooling rate of
200.degree. C./min or less in a temperature region from (annealing
point+30.degree. C.) to (strain point-70.degree. C.).
20. A glass to be tempered, comprising as a glass composition, in
terms of mass %, 45 to 75% of SiO.sub.2, 10 to 25% of
Al.sub.2O.sub.3, 0 to 10% of B.sub.2O.sub.3, 0 to 8% of MgO, 0 to
20% of SrO+BaO, and 0 to 14% of Na.sub.2O.
21. The glass to be tempered according to claim 20, wherein the
glass to be tempered has a thickness of 2 mm or less and has a
thermal shrinkage amount of 250 ppm or less when the glass to be
tempered is subjected to thermal treatment under conditions of
500.degree. C. for 1 hour after being subjected to tempering
treatment involving immersion in KNO.sub.3 at 460.degree. C. for 6
hours.
Description
TECHNICAL FIELD
[0001] The present invention relates to a tempered glass, and more
particularly, to a tempered glass suitable for, for example, a
cover glass for a cellular phone, a digital camera, or a personal
digital assistant (PDA), a substrate or cover glass for a solar
cell such as a thin-film compound solar cell, or a substrate for a
display such as a touch panel display.
BACKGROUND ART
[0002] Devices such as a cellular phone, a digital camera, a PDA, a
touch panel display, and a large-screen television tend to be more
widely used.
[0003] A tempered glass produced by performing tempering treatment
such as ion exchange treatment is used in each of those devices
(see Patent Literature 1 and Non Patent Literature 1).
[0004] In conventional devices, there has been adopted a structure
in which a touch panel sensor is formed on a display module and a
tempered glass (protective member) is placed over the touch panel
sensor.
[0005] Further, although small devices such as a cellular phone
each have a size of 3 to 4 inches in most cases, tablet PCs and the
like each have a size of 9 to 10 inches in most cases.
CITATION LIST
Patent Literature
[0006] Patent Literature 1: JP 2006-83045 A
Non Patent Literature
[0006] [0007] Non Patent Literature 1: Tetsuro Izumitani et al.,
"New glass and physical properties thereof," First edition,
Management System Laboratory. Co., Ltd., Aug. 20, 1984, p.
451-498
SUMMARY OF INVENTION
Technical Problem
[0008] By the way, devices such as tablet PCs are required to have
reduced mass and reduced total thickness in some cases.
[0009] Thus, in order to meet such requirement, a method involving
forming a touch panel sensor on a tempered glass (protective
member) has been being adopted. In this case, the tempered glass is
required to, for example, (1) have a high mechanical strength, (2)
have a liquidus viscosity suitable for, for example, a down-draw
method such as an overflow down-draw method or a slit down-draw
method, or a float method, in order to form a large amount of large
glass to be tempered into a shape, (3) have a viscosity at high
temperature suitable for being formed into a shape, and (4) have a
low density.
[0010] Further, a touch panel is required to be capable of
detecting not only information provided by finger input but also
subtle information provided by pen input or the like. In this case,
the touch panel needs to have a higher resolution capability of a
signal to be detected. That is, a transparent conductive film
formed on the touch panel needs to have a denser wiring pattern. As
a result, many sensors are arranged on the wiring pattern, causing
higher electrical resistance and thus leading to delayed electrical
signal transmission, with the result that feeling of smooth
operation of the tough panel is not achieved.
[0011] When a transparent conductive film such as an ITO film is
formed on a tempered glass under high temperature, the
crystallinity of the transparent conductive film increases, thus
enabling reduced electrical resistance, but, when the tempered
glass is subjected to thermal treatment under high temperature,
there arise problems such as disappearance of a compression stress
and thermal shrinkage of glass, which prevents precise
pattering.
[0012] The present invention has been made in view of the
above-mentioned circumstances. A technical object of the present
invention is to produce a tempered glass which satisfies the
above-mentioned required characteristics (1) to (4) and in which
disappearance of a compression stress and thermal shrinkage are
unlikely to occur even if the tempered glass is subjected to
thermal treatment under high temperature.
Solution to Problem
[0013] The inventors of the present invention have made various
studies. As a result, the inventors have found that the
above-mentioned technical object can be achieved by applying
tempering treatment to a predetermined glass to be tempered,
thereby yielding a tempered glass, and the finding is proposed as
the present invention. That is, a tempered glass according to one
embodiment of the present invention is a tempered glass having a
compression stress layer in a surface thereof, the tempered glass
comprising as a glass composition, in terms of mass %, 45 to 75% of
SiO.sub.2, 10 to 25% of Al.sub.2O.sub.3, 0 to 10% of
B.sub.2O.sub.3, 0 to 8% of MgO, 0 to 20% of SrO+BaO, and 0 to 14%
of Na.sub.2O. Herein, the term "SrO+BaO" refers to the total amount
of SrO and BaO.
[0014] Second, the tempered glass according to the one embodiment
of the present invention is preferably a tempered glass having a
compression stress layer in a surface thereof, the tempered glass
comprising as a glass composition, in terms of mass %, 45 to 75% of
SiO.sub.2, 10 to 25% of Al.sub.2O.sub.3, 0 to 10% of
B.sub.2O.sub.3, 0 to 4% of MgO, 0 to 20% of SrO+BaO, and 0 to 10%
of Na.sub.2O.
[0015] Third, the tempered glass according to the one embodiment of
the present invention is preferably a tempered glass having a
compression stress layer in a surface thereof, the tempered glass
comprising as a glass composition, in terms of mass %, 45 to 63% of
SiO.sub.2, 10 to 25% of Al.sub.2O.sub.3, 0 to 10% of
B.sub.2O.sub.3, 0 to 4% of MgO, 0.1 to 20% of SrO+BaO, and 1 to 10%
of Na.sub.2O.
[0016] Fourth, the tempered glass according to the one embodiment
of the present invention is preferably a tempered glass having a
compression stress layer in a surface thereof, the tempered glass
comprising as a glass composition, in terms of mass %, 45 to 63% of
SiO.sub.2, 10 to 25% of Al.sub.2O.sub.3, 0 to 10% of
B.sub.2O.sub.3, 0 to 4% of MgO, 0.1 to 20% of SrO+BaO, and 1 to 10%
of Na.sub.2O and having a mass ratio (MgO+CaO)/(SrO+BaO) of from
0.1 to 1.5. Herein, the term "MgO+CaO" refers to the total amount
of MgO and CaO.
[0017] Fifth, the tempered glass according to the one embodiment of
the present invention is preferably a tempered glass having a
compression stress layer in a surface thereof, the tempered glass
comprising as a glass composition, in terms of mass %, 45 to 63% of
SiO.sub.2, 10 to 25% of Al.sub.2O.sub.3, 0 to 10% of
B.sub.2O.sub.3, 0 to 3% of MgO, 0.1 to 15% of CaO, 0.1 to 13% of
SrO, 0.1 to 20% of SrO+BaO, and 1 to 8% of Na.sub.2O and having a
mass ratio (MgO+CaO)/(SrO+BaO) of from 0.1 to 1.0.
[0018] Sixth, the tempered glass according to the one embodiment of
the present invention is preferably a tempered glass having a
compression stress layer in a surface thereof, the tempered glass
comprising as a glass composition, in terms of mass %, 45 to 63% of
SiO.sub.2, 10 to 25% of Al.sub.2O.sub.3, 0 to 10% of
B.sub.2O.sub.3, O to less than 2% of MgO, 2 to 15% of CaO, 5 to 13%
of SrO, 0.1 to 8% of BaO, 5.1 to 20% of SrO+BaO, and 1 to 8% of
Na.sub.2O and having a mass ratio (MgO+CaO)/(SrO+BaO) of from 0.1
to 0.8.
[0019] Seventh, the tempered glass according to the one embodiment
of the present invention is preferably a tempered glass having a
compression stress layer in a surface thereof, the tempered glass
comprising as a glass composition, in terms of mass %, 45 to 63% of
SiO.sub.2, 12 to 25% of Al.sub.2O.sub.3, 0 to 10% of
B.sub.2O.sub.3, O to less than 2% of MgO, 2 to 15% of CaO, 8 to 13%
of SrO, 2 to 8% of BaO, 10 to 20% of SrO+BaO, and 1 to 8% of
Na.sub.2O and having a mass ratio (MgO+CaO)/(SrO+BaO) of from 0.1
to 0.5.
[0020] Eighth, in the tempered glass according to the one
embodiment of the present invention, it is preferred that a
compression stress value of the compression stress layer be 300 MPa
or more, and a thickness (stress depth) of the compression stress
layer be 5 .mu.m or more. Herein, the "compression stress value of
the compression stress layer" and the "thickness of the compression
stress layer" can be calculated by observing the number of
interference fringes and each interval between the interference
fringes, with a surface stress meter.
[0021] Ninth, it is preferred that the tempered glass according to
the one embodiment of the present invention have an internal
tensile stress of 50 MPa or less. Herein, the "internal tensile
stress" can be calculated from Equation 1 described below. Note
that the thickness in Equation 1 corresponds to a sheet thickness
in the case of a flat sheet shape.
Internal tensile stress=(compression stress value.times.stress
depth)/(thickness-stress depth.times.2) (Equation 1)
[0022] Tenth, it is preferred that the tempered glass according to
the one embodiment of the present invention have a thermal
expansion coefficient of from 50.times.10.sup.-7 to
100.times.10.sup.-7/.degree. C. Herein, the term "thermal expansion
coefficient" refers to a value obtained through measurement of an
average thermal expansion coefficient in the temperature range of
from 30 to 380.degree. C. with a dilatometer.
[0023] Eleventh, it is preferred that the tempered glass according
to the one embodiment of the present invention have a strain point
of 550.degree. C. or more. Herein, the term "strain point" refers
to a value obtained through measurement based on a method of ASTM
C336.
[0024] Twelfth, it is preferred that the tempered glass according
to the one embodiment of the present invention have a temperature
at a viscosity at high temperature of 10.sup.2.5 dPas of
1,550.degree. C. or less. Herein, the term "temperature at a
viscosity at high temperature of 10.sup.2.5 dPas" refers to a value
obtained through measurement by a platinum sphere pull up
method.
[0025] Thirteenth, it is preferred that the tempered glass
according to the one embodiment of the present invention have a
liquidus temperature of 1,200.degree. C. or less. Herein, the term
"liquidus temperature" refers to a temperature at which crystals of
glass are deposited after glass is pulverized and glass powder that
passes through a standard 30-mesh sieve (sieve opening: 500 .mu.m)
and remains on a 50-mesh sieve (sieve opening: 300 .mu.m) is placed
in a platinum boat and then kept for 24 hours in a gradient heating
furnace.
[0026] Fourteenth, it is preferred that the tempered glass
according to the one embodiment of the present invention have a
liquidus viscosity of 10.sup.3.0 dPas or more. Herein, the term
"liquidus viscosity" refers to a value obtained through measurement
of a viscosity of glass at the liquidus temperature by a platinum
sphere pull up method.
[0027] Fifteenth, it is preferred that the tempered glass according
to the one embodiment of the present invention be used for a
substrate for a solar cell.
[0028] Sixteenth, it is preferred that the tempered glass according
to the one embodiment of the present invention be used for a
substrate for a thin-film compound solar cell.
[0029] Seventeenth, it is preferred that the tempered glass
according to the one embodiment of the present invention be used
for a substrate for a display.
[0030] Eighteenth, it is preferred that the tempered glass
according to the one embodiment of the present invention be formed
into a flat sheet shape by a float method.
[0031] Nineteenth, it is preferred that the tempered glass
according to the one embodiment of the present invention be
manufactured by being cooled at an average cooling rate of
200.degree. C./min or less in a temperature region from (annealing
point+30.degree. C.) to (strain point-70.degree. C.). Herein, the
term "annealing point" refers to a value obtained through
measurement based on a method of ASTM C336.
[0032] Twentieth, a glass to be tempered according to one
embodiment of the present invention comprises as a glass
composition, in terms of mass %, 45 to 75% of SiO.sub.2, 10 to 25%
of Al.sub.2O.sub.3, 0 to 10% of B.sub.2O.sub.3, 0 to 8% of MgO, 0
to 20% of SrO+BaO, and 0 to 14% of Na.sub.2O.
[0033] Twenty-first, it is preferred that the glass to be tempered
according to the one embodiment of the present invention have a
thickness of 2 mm or less and have a thermal shrinkage amount of
250 ppm or less when the glass to be tempered is subjected to
thermal treatment under the conditions of 500.degree. C. for 1 hour
after being subjected to tempering treatment involving immersion in
KNO.sub.3 at 460.degree. C. for 6 hours. Herein, the "thermal
shrinkage amount" can be calculated in accordance with, for
example, the following procedure. As illustrated in FIG. 1, linear
markings 2 are drawn at two sites on a glass 1 having a flat sheet
shape and a distance l.sub.0 between the markings 2 is then
measured. Next, the glass 1 is folded vertically with respect to
the markings 2, thereby dividing the glass 1 into two sample
pieces. Further, after tempering treatment is applied to only one
of the sample pieces, a tempered sample piece 1a and a non-tempered
sample piece 1b are lined up, followed by fixing of the both with
an adhesive tape, and marking shifts .DELTA.L.sub.1 and
.DELTA.L.sub.2 are measured. In the measurement, in the case where
the positions of the markings 2 of the tempered sample piece la are
located inside the positions of the markings 2 of the non-tempered
sample piece 1b, .DELTA.L.sub.1 and .DELTA.L.sub.2 are represented
as positive values, and a volume change amount S1 is calculated by
using Equation 2 described below. Note that the tempering treatment
is carried out by immersing a sample piece in KNO.sub.3 at
460.degree. C. for 6 hours. Subsequently, thermal treatment is
applied only to the tempered glass 1. The thermal treatment is
carried out under the conditions of a temperature rise to
500.degree. C. at +3.degree. C./min, maintenance of the temperature
of 500.degree. C. for 1 hour, and a temperature fall to room
temperature at -3.degree. C./min. After that, the thermally treated
sample piece 1a and the non-thermally treated (and non-tempered)
sample piece 1b are lined up, followed by fixing of the both with
an adhesive tape, and marking shifts .DELTA.L.sub.1 and
.DELTA.L.sub.2 are measured. In the measurement, in the case where
the positions of the markings 2 of the thermally treated sample
piece 1a are located inside the positions of the markings 2 of the
non-thermally treated sample piece 1b, .DELTA.L.sub.1 and
.DELTA.L.sub.2 are represented as positive values, and a volume
change amount S2 is calculated by using Equation 2 described below.
Finally, the thermal shrinkage amount S of the glass to be tempered
is calculated by using Equation 3.
S=[{.DELTA.L.sub.1 (.mu.m)+.DELTA.L.sub.2
(.mu.m)}].times.10.sup.3]/l.sub.o (mm) (Equation 2)
S=S2-S1 (Equation 3)
BRIEF DESCRIPTION OF DRAWINGS
[0034] FIG. 1 is a schematic explanatory diagram illustrating a
measurement method for a thermal shrinkage amount.
DESCRIPTION OF EMBODIMENTS
[0035] A tempered glass according to an embodiment of the present
invention has a compression stress layer in a surface thereof and
comprises as a glass composition, in terms of mass %, 45 to 75% of
SiO.sub.2, 10 to 25% of Al.sub.2O.sub.2, 0 to 10% of
B.sub.2O.sub.3, 0 to 8% of MgO, 0 to 14% of Na.sub.2O, and 0 to 20%
of SrO+BaO.
[0036] A physical tempering method may be chosen as a method of
forming the compression stress layer in the surface of the glass,
but it is more preferred that a chemical tempering method be
chosen. The chemical tempering method is a method comprising
introducing alkali ions each having a large ion radius into the
vicinity of a surface of glass by performing ion exchange at a
temperature equal to or lower than the strain point of the glass.
When the chemical tempering method is used to form the compression
stress layer, a desired compression stress layer can be formed even
if the glass has a thin thickness. In addition, even when the
compression stress layer is formed by the chemical tempering method
and then the resultant tempered glass is cut, the tempered glass
does not easily break unlike tempered glass produced by applying a
physical tempering method such as an air cooling tempering
method.
[0037] The ion exchange treatment can be performed by, for example,
immersing glass in a KNO.sub.3 molten salt at 400 to 550.degree. C.
for to 24 hours. As conditions for the ion exchange, optimum
conditions may be selected in view of, for example, the viscosity
characteristics, applications, thickness, and internal tensile
stress of glass. Note that when the ion exchange of K ions in the
KNO.sub.3 molten salt with Na components in the glass is performed,
it is possible to form efficiently the compression stress
layer.
[0038] The reasons why the content range of each component in the
glass composition in the tempered glass of this embodiment has been
restricted as mentioned above are described below.
[0039] SiO.sub.2 is a component that forms a network of glass. The
content of SiO.sub.2 is 45 to 75%, preferably 45 to 70%, more
preferably 45 to 63%, still more preferably 48 to 60%, most
preferably 50 to 58%. When the content of SiO.sub.2 is too large,
melting and forming become difficult, and a thermal expansion
coefficient becomes too low, with the result that matching of the
thermal expansion coefficient with those of peripheral materials
becomes difficult. On the other hand, when the content of SiO.sub.2
is too small, vitrification becomes difficult, and the thermal
expansion coefficient becomes too high, with the result that
thermal shock resistance is liable to lower.
[0040] Al.sub.2O.sub.3 is a component that enhances ion exchange
performance, and is a component that enhances a strain point and a
Young's modulus. The content of Al.sub.2O.sub.3 is 10 to 25%. When
the content of Al.sub.2O.sub.3 is too large, a devitrified crystal
is liable to deposit in the glass and forming of the glass becomes
difficult. Further, when the content of Al.sub.2O.sub.3 is too
large, the thermal expansion coefficient becomes too low, with the
result that matching of the thermal expansion coefficient with
those of peripheral materials becomes difficult, and its viscosity
at high temperature rises, with the result that it becomes
difficult to melt the glass. On the other hand, when the content of
Al.sub.2O.sub.3 is too small, ion exchange performance may not be
sufficiently exhibited. The lower limit range of Al.sub.2O.sub.3 is
suitably 11% or more, 12% or more, and the upper limit range of
Al.sub.2O.sub.3 is suitably 22% or less, 20% or less, 18% or less,
16% or less, 15% or less.
[0041] B.sub.2O.sub.3 is a component that has an effect of lowering
the viscosity at high temperature and density, and has effects of
stabilizing glass so that a crystal may be unlikely to be
precipitated, and lowering the liquidus temperature. The content of
B.sub.2O.sub.3 is 0 to 10%, preferably 0 to 5%, more preferably 0
to 3%, still more preferably 0 to 1%, and it is desirable that the
glass be substantially free of B.sub.2O.sub.3. Herein, the phrase
"substantially free of B.sub.2O.sub.3" refers to the case where the
content of B.sub.2O.sub.3 in the glass composition is less than 0.1
mass %. When the content of B.sub.2O.sub.3 is too large, the strain
point lowers, ion exchange treatment causes weathering to occur in
a surface of the glass, the water resistance deteriorates, and the
thickness of the compression stress layer tends to be smaller.
[0042] MgO is a component that lowers the viscosity at high
temperature to enhance meltability and formability, or to enhance
the strain point and the Young's modulus, and is a component that
shows a particularly high effect of improving the ion exchange
performance, among alkaline earth metal oxides. The content of MgO
is 0 to 8%, preferably 0 to 4%, more preferably 0 to 3%, still more
preferably 0 to 2%, particularly preferably 0.01 to 1%, most
preferably 0.05 to 1%. However, when the content of MgO becomes too
large, the density and the thermal expansion coefficient increase
improperly, and the glass is liable to be devitrified.
[0043] Na.sub.2O is an ion exchange component, is a component that
lowers the viscosity at high temperature to enhance the meltability
and the formability, and is a component that improves
devitrification resistance. The content of Na.sub.2O is 0 to 14%,
preferably 0 to 10%, more preferably 1 to 10%, still more
preferably 1 to 8%, still more preferably 2 to 8%, particularly
preferably 3 to less than 7%, most preferably 4 to 6.5%. When the
content of Na.sub.2O is too large, the thermal expansion
coefficient becomes too high, and hence, the thermal shock
resistance lowers, and matching of the thermal expansion
coefficient with those of peripheral materials becomes difficult.
Further, when the content of Na.sub.2O is too large, the strain
point lowers excessively, and the component balance in the glass
composition is impaired, with the result that the devitrification
resistance tends to deteriorate rather than improve. On the other
hand, when the content of Na.sub.2O is too small, the meltability
deteriorates, the thermal expansion coefficient becomes too low,
and the ion exchange performance is liable to deteriorate.
[0044] SrO is a component that reduces the viscosity at high
temperature to increase the meltability and formability, and
increases the strain point and Young's modulus. However, when the
content of SrO is too large, the ion exchange performance tends to
deteriorate, the density and thermal expansion coefficient
improperly increase, and the glass is liable to devitrify. Thus,
the content of SrO is preferably 0 to 15%, 0.1 to 13%, 2 to 13%, 5
to 13%, 7 to 13%, 8 to 13%, particularly preferably 9 to 12%.
[0045] BaO is a component that reduces the viscosity at high
temperature to increase the meltability and formability, and
increases the strain point and Young's modulus. However, when the
content of BaO is too large, the ion exchange performance tends to
deteriorate, the density and thermal expansion coefficient
improperly increase, and the glass is liable to devitrify. Thus,
the content of BaO is preferably 0 to 12%, 0.1 to 10%, 0.1 to 9%,
0.1 to 8%, 1 to 8%, 2 to 8%, particularly preferably 3 to 8%.
[0046] SrO+BaO is a component that reduces the viscosity at high
temperature to increase the meltability and formability, and
increases the strain point and Young's modulus. The content of
SrO+BaO is 0 to 20%. When the content of SrO+BaO is large, the ion
exchange performance tends to deteriorate, the density and thermal
expansion coefficient increase, and the glass is liable to
devitrify. However, when the content of SrO+BaO is small, the
above-mentioned effects are poorly provided. The content range of
SrO+BaO is suitably 0.1 to 20%, 2 to 20%, 5.1 to 20%, 10 to 20%, 12
to 18%, particularly suitably 13 to 17%.
[0047] In addition to the components described above, the following
components may be added.
[0048] CaO is a component that reduces the viscosity at high
temperature to increase the meltability and formability, and
increases the strain point and Young's modulus, is a component that
shows a particularly high effect of enhancing the ion exchange
performance among alkaline earth metal oxides, and is also a
component that increases the denitrification resistance. The
content of CaO is preferably 0.1 to 15%, 1 to 15%, 2 to 11%, 3 to
9%, particularly preferably 4 to 7%. When the content of CaO is too
large, the density and thermal expansion coefficient improperly
increase, and the component balance in the glass composition is
impaired, with the result that the glass is liable to denitrify and
the ion exchange performance tends to deteriorate.
[0049] A mass ratio (MgO+CaO)/(SrO+BaO) is preferably 0 to 1. When
the mass ratio (MgO+CaO)/(SrO+BaO) is restricted within a proper
range, a high liquidus viscosity is easily maintained while a high
strain point is maintained. The lower limit range of the mass ratio
(MgO+CaO)/(SrO+BaO) is suitably 0.1 or more, 0.2 or more, 0.3 or
more, particularly suitably 0.4 or more, and the upper limit range
thereof is suitably 0.9 or less, 0.8 or less, 0.7 or less,
particularly suitably 0.6 or less.
[0050] MgO+CaO+SrO+BaO is a component that reduces the viscosity at
high temperature without reducing the strain point excessively.
When the content thereof is too large, the density and thermal
expansion coefficient improperly increase, the denitrification
resistance is liable to deteriorate, and the ion exchange
performance is liable to deteriorate. Thus, the content of
MgO+CaO+SrO+BaO is preferably 10 to 30%, 13 to 27%, 15 to 25%, 17
to 23%, 18 to 22%, particularly preferably 19 to 21%. Note that the
term "MgO+CaO+SrO+BaO" refers to the total amount of MgO, CaO, SrO,
and BaO.
[0051] Li.sub.2O is an ion exchange component and is a component
that reduces the viscosity at high temperature to increase the
meltability and formability. Further, Li.sub.2O is a component that
increases the Young's modulus and a component that shows a high
effect of increasing the compression stress value among alkali
metal oxides. However, when the content of Li.sub.2O is too large,
the liquidus viscosity lowers, the glass is liable to denitrify,
and the thermal expansion coefficient becomes too high, with the
result that the thermal shock resistance deteriorates and it
becomes difficult to match the thermal expansion coefficient with
those of peripheral materials. In addition, when the content of
Li.sub.2O is too large, the viscosity at low temperature reduces
excessively, and the stress relaxation is liable to occur, with the
result that the compression stress value lowers rather than
increases in some cases. Thus, the content of Li.sub.2O is
preferably 0 to 10%, 0 to 5%, 0 to 1%, particularly preferably 0 to
0.5%, and it is desirable that the glass be substantially free of
Li.sub.2O. Herein, the phrase "substantially free of Li.sub.2O"
refers to the case where the content of Li.sub.2O in the glass
composition is less than 0.1%.
[0052] K.sub.2O is a component that promotes ion exchange and is a
component that shows a high effect of increasing the thickness of
the compression stress layer among alkali metal oxides. In
addition, K.sub.2O is a component that reduces the viscosity at
high temperature to increase the meltability and formability and is
also a component that improves the devitrification resistance.
However, when the content of K.sub.2O is too large, the thermal
expansion coefficient becomes improperly high, the thermal shock
resistance deteriorates, and it becomes difficult to match the
thermal expansion coefficient with those of peripheral materials.
Further, when the content of K.sub.2O is too large, the strain
point lowers excessively, and the component balance in the glass
composition is impaired, with the result that the devitrification
resistance tends to deteriorate rather than improve. In view of the
above-mentioned circumstances, the content of K.sub.2O is
preferably 0 to 15%, 0.5 to 13%, 2 to 10%, 3 to 9%, particularly
preferably 3 to 7%.
[0053] Li.sub.2O+Na.sub.2O+K.sub.2O is an ion exchange component
and is a component that reduces the viscosity at high temperature
to increase the meltability and formability. When the content of
Li.sub.2O+Na.sub.2O+K.sub.2O is too large, the glass is liable to
denitrify, and the thermal expansion coefficient becomes too high,
with the result that the thermal shock resistance deteriorates and
it becomes difficult to match the thermal expansion coefficient
with those of peripheral materials. Moreover, when the content of
Li.sub.2O+Na.sub.2O+K.sub.2O is too large, the strain point lowers
excessively, with the result that a high compression stress value
is difficult to be achieved in some cases, and when thermal
treatment is applied to the glass at high temperature, the
compression stress of the glass is liable to disappear. In
addition, when the content of Li.sub.2O+Na.sub.2O+K.sub.2O is too
large, the viscosity at around the liquidus temperature reduces,
with the result that it is difficult to attain a high liquidus
viscosity in some cases. Thus, the content of
Li.sub.2O+Na.sub.2O+K.sub.2O is preferably 20% or less, 18% or
less, 15% or less, 13% or less, particularly preferably 12% or
less. On the other hand, when the content of
Li.sub.2O+Na.sub.2O+K.sub.2O is too small, the ion exchange
performance and meltability are liable to deteriorate. Thus, the
content of Li.sub.2O+Na.sub.2O+K.sub.2O is preferably 3% or more,
5% or more, 7% or more, 8% or more, particularly preferably 9% or
more. Note that the term "Li.sub.2O+Na.sub.2O+K.sub.2O" refers to
the total amount of Li.sub.2O, Na.sub.2O, and K.sub.2O.
[0054] ZrO.sub.2 is a component that remarkably enhances the ion
exchange performance and increases the viscosity around the
liquidus viscosity and the strain point. The content of ZrO.sub.2
is preferably 0 to 15%, 0 to 10%, 0.001 to 10%, 0.1 to 9%, 2 to 8%,
particularly preferably 2.5 to 5%. When the content of ZrO.sub.2 is
too large, the denitrification resistance extremely deteriorates in
some cases.
[0055] P.sub.2O.sub.5 is a component that enhances the ion exchange
performance and a component that shows a particularly high effect
of increasing the thickness of the compression stress layer. The
content of P.sub.2O.sub.5 is preferably 10% or less, 8% or less, 6%
or less, 4% or less, 2% or less, particularly preferably 0.5% or
less. When the content of P.sub.2O.sub.5 is too large, phase
separation occurs in the glass and the water resistance is liable
to deteriorate.
[0056] Fe.sub.2O.sub.3 is a component that is comprised as an
impurity in raw materials and is a component that acts as a fining
agent. The content of Fe.sub.2O.sub.3 is preferably 0 to 2%, 0 to
1%, 0 to 0.5%, 0 to 0.1%, particularly preferably 0.001 to 0.05%.
When the content of Fe.sub.2O.sub.3 is too large, the glass is
liable to be colored and to devitrify. Note that, in order to
reduce the content of Fe.sub.2O.sub.3 extremely, a high-purity raw
material needs to be used, which significantly increases the batch
cost.
[0057] TiO.sub.2 is a component that enhances the ion exchange
performance and is a component that reduces the viscosity at high
temperature. However, when the content thereof is too large, the
glass is liable to be colored and to devitrify. The content of
TiO.sub.2 is preferably 0 to 5%, 0 to 4%, 0 to 1%, particularly
preferably 0 to 0.1%, and it is desirable that the glass be
substantially free of TiO.sub.2. Herein, the phrase "substantially
free of TiO.sub.2" refers to the case where the content of
TiO.sub.2 in the glass composition is 0.01% or less.
[0058] ZnO is a component that enhances the ion exchange
performance and is a component that shows a particularly high
effect of increasing the compression stress value. Further, ZnO is
a component that reduces the viscosity at high temperature without
reducing the viscosity at low temperature. When the content of ZnO
is too large, phase separation occurs in the glass, the
devitrification resistance deteriorates, the density improperly
increases, and the thickness of the compression stress layer tends
to decrease. Thus, the content of ZnO is preferably 0 to 6%, 0 to
5%, 0 to 3%, particularly preferably 0 to 1%, and it is desirable
that the glass be substantially free of ZnO. Herein, the phrase
"substantially free of ZnO" refers to the case where the content of
ZnO in the glass composition is 0.1% or less.
[0059] It is possible to use, as a fining agent, one kind or two or
more kinds selected from the group consisting of SnO.sub.2,
CeO.sub.2, Cl, and SO.sub.3. The total content of these components
is preferably 0 to 3%, 0.001 to 1%, 0.01 to 0.5%, particularly
preferably 0.05 to 0.4%. When the content of these components is
too large, the devitrification resistance is liable to deteriorate.
Among these components, SnO.sub.2 and SO.sub.3 are particularly
preferably used from the viewpoint of a fining effect. The content
of SnO.sub.2 is preferably 0 to 1%, 0.01 to 0.5%, particularly
preferably 0.05 to 0.4%. The content of SO.sub.3 is preferably 0 to
1%, 0.01 to 0.5%, particularly preferably 0.03 to 0.4%.
[0060] Rare earth oxides such as Nb.sub.2O.sub.5 and
La.sub.2O.sub.3 are components that increase the Young's modulus.
However, the costs of the raw materials themselves thereof are
high, and when the rare earth oxides are comprised in a large
amount, the devitrification resistance is liable to deteriorate.
Thus, the total content of the rare earth oxides is preferably 3%
or less, 2% or less, 1% or less, 0.5% or less, particularly
preferably 0.1% or less.
[0061] Transition metal oxides such as Co and Ni are components
that cause the intense coloration of glass, thereby reducing the
transmittance of the glass. When the total content of the
transition metal oxides is too large in a tempered glass used for a
solar cell, the photoelectric conversion efficiency of the solar
cell is particularly liable to deteriorate. Thus, it is desirable
that the use amounts of glass raw materials (including cullet) be
adjusted so that the total content of the transition metal oxides
is preferably 0.5% or less, 0.1% or less, particularly preferably
0.05% or less.
[0062] It is desirable that the glass be substantially free of
As.sub.2O.sub.3, Sb.sub.2O.sub.3, PbO, Bi.sub.2O.sub.3, and F,
because they are components that may adversely affect the
environment. Herein, the phrase "substantially free of
As.sub.2O.sub.3" refers to the case where the content of
As.sub.2O.sub.3 in the glass composition is less than 0.01%. The
phrase "substantially free of Sb.sub.2O.sub.3" refers to the case
where the content of Sb.sub.2O.sub.3 in the glass composition is
less than 0.01%. The phrase "substantially free of PbO" refers to
the case where the content of PbO in the glass composition is less
than 0.1%. The phrase "substantially free of Bi.sub.2O.sub.3"
refers to the case where the content of Bi.sub.2O.sub.3 in the
glass composition is less than 0.1%. The phrase "substantially free
of F" refers to the case where the content of F in the glass
composition is less than 0.1%.
[0063] In addition to the above-mentioned components, other
components may be added, for example, up to 10%, in particular, up
to 5%.
[0064] The tempered glass of this embodiment has a thermal
expansion coefficient of preferably 50.times.10.sup.-7 to
100.times.10.sup.-7/.degree. C., 70.times.10.sup.-7 to
100.times.10.sup.-7/.degree. C., 75.times.10.sup.-7 to
95.times.10.sup.-7/.degree. C., particularly preferably
80.times.10.sup.-7 to 90.times.10.sup.-7/.degree. C. With this, the
rate of breakage caused by rapid temperature change can be reduced
at the time of tempering treatment, and it becomes easy to match
the thermal expansion coefficient with those of members such as an
ITO film, thus easily preventing failures such as film peeling.
Note that the thermal expansion coefficient can be increased by
increasing the content of an alkali metal oxide or an alkaline
earth metal oxide in the glass composition, and in contrast, the
thermal expansion coefficient can be decreased by reducing the
content of an alkali metal oxide or an alkaline earth metal oxide
in the glass composition.
[0065] The tempered glass of this embodiment has a density of
preferably 3 g/cm.sup.3 or less, 2.9 g/cm.sup.3 or less,
particularly preferably 2.85 g/cm.sup.3 or less. As the density
becomes smaller, the weight of the tempered glass can be reduced
more. Note that the density can be decreased by increasing the
content of SiO.sub.2, P.sub.2O.sub.s, or B.sub.2O.sub.3 in the
glass composition or reducing the content of an alkali metal oxide,
an alkaline earth metal oxide, ZnO, ZrO.sub.2, or TiO.sub.2 in the
glass composition. Herein, the term "density" refers to a value
obtained through measurement by the well-known Archimedes
method.
[0066] The tempered glass of this embodiment has a strain point of
preferably 580.degree. C. or more, 600.degree. C. or more,
610.degree. C. or more, particularly preferably 620.degree. C. or
more. The strain point is a characteristic serving as an index for
heat resistance. As the strain point becomes higher, the
disappearance of the compression stress is more unlikely to occur
even when the tempered glass is subjected to thermal treatment at
high temperature and the tempered glass can more easily maintain
its mechanical strength. Further, as the strain point becomes
higher, the tempered glass resists thermal shrinkage more even if
the tempered glass is subjected to thermal treatment at high
temperature. In addition, as the strain point becomes higher,
stress relaxation is more unlikely to occur at the time of ion
exchange, and hence a higher compression stress value can be
provided. Note that the strain point can be increased by reducing
the content of an alkali metal oxide in the glass composition or
increasing the content of an alkaline earth metal oxide,
Al.sub.2O.sub.3, ZrO.sub.2, or P.sub.2O.sub.5 in the glass
composition.
[0067] The tempered glass of this embodiment has a temperature at a
viscosity at high temperature of 10.sup.2.5 dPas of preferably
1,600.degree. C. or less, 1,570.degree. C. or less, 1,530.degree.
C. or less, 1,500.degree. C. or less, 1,480.degree. C. or less,
particularly preferably 1,450.degree. C. or less. The temperature
at a viscosity at high temperature of 10.sup.2.5 dPas corresponds
to the melting temperature of glass. As the temperature at a
viscosity at high temperature of 10.sup.2.5 dPas becomes lower, the
glass can be melted at lower temperature. Further, as the
temperature at a viscosity at high temperature of 10.sup.2.5 dPas
becomes lower, a smaller burden is given to glass production
equipment such as a melting furnace, and the bubble quality of the
glass can be enhanced. As a result, the tempered glass can be
produced at lower cost. Note that the temperature at a viscosity at
high temperature of 10.sup.2.5 dPas can be decreased by increasing
the content of an alkali metal oxide, an alkaline earth metal
oxide, ZnO, B.sub.2O.sub.3, or TiO.sub.2 or reducing the content of
SiO.sub.2 or Al.sub.2O.sub.3.
[0068] The tempered glass of this embodiment has a liquidus
temperature of preferably 1,200.degree. C. or less, 1,180.degree.
C. or less, 1,150.degree. C. or less, 1,120.degree. C. or less,
1,100.degree. C. or less, particularly preferably 1080.degree. C.
or less. As the liquidus temperature becomes lower, the
devitrification resistance and formability are improved more. Note
that the liquidus temperature can be decreased by increasing the
content of Na.sub.2O, K.sub.2O, or B.sub.2O.sub.3 in the glass
composition or by reducing the content of Al.sub.2O.sub.3,
Li.sub.2O, MgO, ZnO, TiO.sub.2, or ZrO.sub.2 in the glass
composition.
[0069] The tempered glass of this embodiment has a liquidus
viscosity of preferably 10.sup.4.0 dPas or more, 10.sup.4.2 dPas or
more, 10.sup.4.3 dPas or more, 10.sup.4.5 dPas or more, 10.sup.4.7
dPas or more, particularly preferably 10.sup.4.9 dPas or more. As
the liquidus viscosity becomes higher, the devitrification
resistance and formability are improved more. Note that the
liquidus viscosity can be increased by increasing the content of
Na.sub.2O or K.sub.2O in the glass composition or by reducing the
content of Al.sub.2O.sub.3, Li.sub.2O, MgO, ZnO, TiO.sub.2, or
ZrO.sub.2 in the glass composition.
[0070] The compression stress value of the compression stress layer
in the tempered glass of this embodiment is preferably 300 MPa or
more, 400 MPa or more, 500 MPa or more, particularly preferably 600
MPa or more. As the compression stress value of the compression
stress layer becomes larger, the mechanical strength of the
tempered glass increases. On the other hand, when an extremely
large compression stress is formed in the tempered glass, micro
cracks are generated in the surface thereof, with the result that
the mechanical strength of the tempered glass may reduce rather
than increases. Further, when an extremely large compression stress
is formed in the tempered glass, an internal tensile stress may
extremely increase. Thus, the compression stress value of the
compression stress layer is preferably 1,300 MPa or less, 1,000 MPa
or less, 900 MPa or less, 800 MPa or less, particularly preferably
700 MPa or less. Note that the compression stress value of the
compression stress layer can be increased by increasing the content
of Al.sub.2O.sub.3, TiO.sub.2, ZrO.sub.2, MgO, or ZnO in the glass
composition or reducing the content of SrO or BaO in the glass
composition. Further, the compression stress value of the
compression stress layer can be increased by shortening an
ion-exchange time or lowering an ion-exchange temperature.
[0071] The thickness of the compression stress layer in the
tempered glass of this embodiment is preferably 5 .mu.m or more, 10
.mu.m or more, 15 .mu.m or more, 20 .mu.m or more, particularly
preferably 30 .mu.m or more. As the thickness of the compression
stress layer becomes larger, the tempered glass is more unlikely to
break even when the tempered glass has a deep flaw. On the other
hand, when the compression stress layer has too large a thickness,
the tempered glass is more difficult to be cut and processed. Thus,
the thickness of the compression stress layer is preferably 100
.mu.m or less, 80 .mu.m or less, 60 .mu.m or less, 50 .mu.m or
less, particularly preferably 40 .mu.m or less. Note that the
thickness of the compression stress layer can be increased by
increasing the content of K.sub.2O or P.sub.2O.sub.5 in the glass
composition or reducing the content of SrO or BaO in the glass
composition. Further, the thickness of the compression stress layer
can be increased by lengthening an ion-exchange time or raising an
ion-exchange temperature. Note that, in order to form the
above-mentioned compression stress layer, ion exchange treatment is
preferably performed in a KNO.sub.3 molten salt at 400 to
550.degree. C. for 2 to 24 hours, in particular, 10 to 18
hours.
[0072] The tempered glass of this embodiment has an internal
tensile stress of preferably 50 MPa or less, 40 MPa or less, 30 MPa
or less, particularly preferably 25 MPa or less. As the internal
tensile stress becomes smaller, it is more unlikely that the
tempered glass is broken by defects inside the tempered glass, and
a cutting failure is more unlikely to occur when the tempered glass
is cut. However, when the tempered glass has an extremely small
internal tensile stress, the compression stress value and stress
depth in the surface of the tempered glass reduce, with the result
that the mechanical strength of the tempered glass is liable to
deteriorate. Thus, the internal tensile stress is preferably 5 MPa
or more, 10 MPa or more, particularly preferably 15 MPa or
more.
[0073] When the tempered glass of this embodiment is used as a
substrate or a cover glass, the tempered glass preferably has an
unpolished surface, and the average surface roughness (Ra) of the
unpolished surface is preferably 10 .ANG. or less, 5 .ANG. or less,
particularly preferably 2 .ANG. or less. Herein, the term "average
surface roughness (Ra)" refers to a value obtained by a measurement
method in accordance with SEMI D7-94 "FPD glass substrate surface
roughness measurement method." The theoretical strength of glass is
very high intrinsically, but glass is often broken even by a stress
far lower than the theoretical strength. This is because, in some
steps after the glass is formed into a shape, such as a polishing
step, a small defect called Griffith flaw is produced in the
surfaces of the glass. Thus, when the surface of the tempered glass
is not polished, the mechanical strength that glass intrinsically
has is more unlikely to be impaired, and hence the tempered glass
is more unlikely to break. In addition, when the surface of the
tempered glass is not polished, the production cost of the tempered
glass can be reduced, because the polishing step thereof can be
eliminated. Moreover, when the entire surface of the tempered glass
is unpolished (excluding a cutting surface), the tempered glass is
much more unlikely to break. Besides, in order to prevent the
tempered glass from breaking from its cutting surface, a chamfering
process or the like may be applied to the cutting surface. Note
that glass formation by an overflow down-draw method can yield an
unpolished glass having a flat sheet shape and a good surface
precision.
[0074] When the tempered glass of this embodiment is used as a
substrate or a cover glass, the tempered glass has a thickness of
preferably 3.0 mm or less, 1.5 mm or less, 1.0 mm or less, 0.7 mm
or less, 0.5 mm or less, particularly preferably 0.3 mm or less. As
the thickness becomes thinner, the tempered glass can have a
lighter weight. Besides, the tempered glass of this embodiment has
the advantage that it is unlikely to break even if it has a thin
thickness. That is, as the thickness becomes thinner, the effect
provided by the present invention is exhibited more significantly.
Note that glass formation by an overflow down-draw method can yield
a glass sheet having a good surface precision and can easily yield
a glass sheet having a thin thickness.
[0075] When the tempered glass of this embodiment is subjected to
thermal treatment under the conditions of 500.degree. C. for 1
hour, the tempered glass has a thermal shrinkage amount of
preferably 250 ppm or less, 200 ppm or less, 180 ppm or less, 150
ppm or less, 130 ppm or less, 110 ppm or less, 80 ppm or less,
particularly preferably 60 ppm or less. It is difficult to pattern
a high-definition ITO film or the like on a tempered glass having
too large a thermal shrinkage amount, and hence, for example, an
operation failure of a touch sensor may be caused. Herein, the
"thermal treatment" is calculated as described below. As
illustrated in FIG. 1, linear markings are drawn at two sites on a
tempered glass and a distance l.sub.0 between the markings is then
measured. Next, the tempered glass is folded vertically with
respect to the markings, thereby dividing the tempered glass into
two sample pieces. Thermal treatment is applied to only one of the
sample pieces. The thermal treatment is carried out under the
conditions of a temperature rise to 500.degree. C. at +3.degree.
C./min, maintenance of the temperature of 500.degree. C. for 1
hour, and a temperature fall to room temperature at -3.degree.
C./min. After that, the thermally treated sample piece and the
non-thermally treated sample piece are lined up, followed by fixing
of the both with an adhesive tape, and marking shifts
.DELTA.L.sub.1 and .DELTA.L.sub.2 are measured. In the measurement,
in the case where the positions of the markings of the thermally
treated sample piece are located inside the positions of the
markings of the non-thermally treated sample piece, .DELTA.L.sub.1
and .DELTA.L.sub.2 are represented as positive values, and a volume
change amount is calculated by using Equation 2 described
above.
[0076] A glass to be tempered according to an embodiment of the
present invention comprises as a glass composition, in terms of
mass %, 45 to 75% of SiO.sub.2, 10 to 25% of Al.sub.2O.sub.2, 0 to
10% of B.sub.2O.sub.3, 0 to 8% of MgO, 0 to 20% of SrO+BaO, and 0
to 14% of Na.sub.2O. The technical features (suitable component
ranges, suitable characteristics, suitable aspects, and the like)
of the glass to be tempered of this embodiment are, in principle,
the same as the technical features of the tempered glass of the
above-mentioned embodiment.
[0077] The glass to be tempered of this embodiment can be produced
by loading glass raw materials blended so as to have a
predetermined glass composition, into a continuous melting furnace,
followed by melting under heating at 1,500 to 1,600.degree. C.,
fining the resultant molten glass, forming the fined molten glass
into a shape with a forming apparatus, and annealing the glass in
an annealing apparatus.
[0078] A float method is preferably adopted as a forming method.
The float method can be used to form a large amount of glass into a
shape at low cost and to form a large glass easily. Further, when
the float method is adopted, the above-mentioned cooling rate can
be easily set, and hence the thermal shrinkage of the glass to be
tempered can be easily reduced. In addition to the float method,
various forming methods can be adopted. It is possible to adopt a
forming method such as a down-draw method (e.g., an overflow
down-draw method, a slot down method, or a re-draw method), a float
method, a roll out method, or a press method. Particularly when the
overflow down-draw method is adopted for glass formation, an
unpolished glass having a good surface precision can be
manufactured efficiently. When the press method is adopted for
glass formation, a small glass can be manufactured efficiently.
[0079] The glass to be tempered of this embodiment is preferably
cooled, in the temperature region from (annealing point+30.degree.
C.) to (strain point-70.degree. C.), at an average cooling rate of
200.degree. C./min or less, 150.degree. C./min or less, 100.degree.
C./min or less, in particular, 80.degree. C./min or less. If the
glass to be tempered is cooled at too fast an average cooling rate,
when the glass to be tempered is subjected to thermal treatment,
the thermal shrinkage amount of the glass to be tempered becomes
larger, and when the tempered glass is subjected to thermal
treatment, the thermal shrinkage amount of the tempered glass
becomes larger. Note that, from the viewpoint of production cost,
the cooling is preferably performed successively after glass
formation and is preferably performed in an annealing furnace.
[0080] When the glass to be tempered of this embodiment is
subjected to ion exchange treatment in a KNO.sub.3 molten salt at
460.degree. C. for 10 hours, the resultant compression stress layer
has a compression stress value of preferably 300 MPa or more, 500
MPa or more, particularly preferably 600 MPa or more, and the
compression stress layer has a thickness of preferably 5 .mu.m or
more, 10 .mu.m or more, particularly preferably 15 .mu.m or
more.
[0081] When the glass to be tempered of this embodiment is
subjected to thermal treatment under the conditions of 500.degree.
C. for 1 hour after being subjected to tempering treatment
(immersed in KNO.sub.3 at 460.degree. C. for 6 hours), the
resultant tempered glass has a thermal shrinkage amount of
preferably 250 ppm or less, 200 ppm or less, 180 ppm or less, 150
ppm or less, 130 ppm or less, 110 ppm or less, 80 ppm or less,
particularly preferably 60 ppm or less. It is difficult to pattern
a high-definition ITO film or the like on a tempered glass having
too large a thermal shrinkage amount, and hence, for example, an
operation failure of a touch sensor may be caused.
[0082] Note that the glass to be tempered may be cut and processed
before tempering treatment, but from the viewpoint of production
cost, the tempered glass is preferably cut and processed after
tempering treatment.
Example 1
[0083] Hereinafter, Examples of the present invention are
described. Note that Examples below are merely illustrative. The
present invention is by no means limited to Examples below.
[0084] Tables 1 to 5 show Examples of the present invention
(Samples Nos. 1 to 33) and Comparative Example (Sample No. 34).
TABLE-US-00001 TABLE 1 No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 No. 7
Glass SiO.sub.2 51.0 51.0 51.0 52.0 53.0 53.0 53.5 composition
Al.sub.2O.sub.3 13.0 13.0 13.0 13.0 13.0 13.0 12.4 (wt %)
B.sub.2O.sub.3 -- -- -- -- -- -- -- MgO 0.1 0.1 0.1 0.1 0.1 0.1 0.1
CaO 7.1 5.4 5.4 5.4 5.4 5.4 5.1 SrO 11.9 13.6 11.9 9.1 9.1 9.1 11.2
BaO 3.5 3.5 5.2 6.3 6.3 6.7 3.3 Li.sub.2O -- -- -- -- -- -- --
Na.sub.2O 4.3 4.3 4.3 4.3 4.3 4.3 5.7 K.sub.2O 4.3 4.3 4.3 6.0 6.0
5.6 4.1 ZrO.sub.2 4.6 4.6 4.6 3.6 2.6 2.6 4.4 Fe.sub.2O.sub.3 0.10
0.10 0.10 0.10 0.10 0.10 0.10 SnO.sub.2 -- 0.10 -- 0.10 -- -- --
SO.sub.3 0.10 -- 0.10 -- 0.10 0.10 0.10 Thermal expansion
coefficient 80 80 80 83 83 83 81 [.times.10.sup.-7/.degree. C.]
Density [g/cm.sup.3] 2.83 2.84 2.84 2.80 2.79 2.80 2.79 Strain
point [.degree. C.] Not 647 645 631 624 625 627 measured Annealing
point [.degree. C.] Not 694 692 679 671 672 674 measured Softening
point [.degree. C.] Not 891 892 881 874 875 875 measured 10.sup.4
dPa s [.degree. C.] 1,168 1,178 1,181 1,187 1,185 1,187 1,176
10.sup.3 dPa s [.degree. C.] 1,313 1,326 1,331 1,347 1,348 1,350
1,333 10.sup.2.5 dPa s [.degree. C.] 1,408 1,423 1,428 1,453 1,455
1,457 1,437 Liquidus temperature [.degree. C.] 1,150 1,140 1,135
1,126 1,131 1,123 1,124 Liquidus viscosity log.sub.10.eta. 4.2 4.3
4.4 4.5 4.4 4.5 4.4 [dPa s] Compression stress value Not Not Not
Not Not Not Not [MPa] measured measured measured measured measured
measured measured Stress layer depth [.mu.m] Not Not Not Not Not
Not Not measured measured measured measured measured measured
measured Compression stress value [MPa] Not Not Not Not Not Not Not
(after thermal treatment measured measured measured measured
measured measured measured at 540.degree. C. for 20 minutes) Stress
layer depth [.mu.m] Not Not Not Not Not Not Not (after thermal
treatment measured measured measured measured measured measured
measured at 540.degree. C. for 20 minutes) Thermal shrinkage amount
Not Not Not Not Not Not Not (500.degree. C.) [ppm] measured
measured measured measured measured measured measured
TABLE-US-00002 TABLE 2 No. 8 No. 9 No. 10 No. 11 No. 12 No. 13 No.
14 Glass SiO.sup.2 51.0 50.8 51.0 52.8 52.5 51.0 51.0 composition
Al.sub.2O.sub.3 13.0 13.0 13.0 13.0 13.0 13.0 13.0 (wt %)
B.sub.2O.sub.3 -- -- -- -- -- -- -- MgO 0.1 0.1 1.0 1.0 0.1 1.0 1.0
CaO 5.4 5.4 4.5 6.5 5.4 6.5 4.5 SrO 11.9 10.9 6.9 9.1 11.9 9.1 11.9
BaO 3.5 4.5 8.5 4.3 3.5 4.3 3.5 Li.sub.2O -- -- -- -- -- -- --
Na.sub.2O 6.0 5.8 5.0 5.0 6.0 5.0 5.0 K.sub.2O 4.3 4.6 5.3 5.3 4.3
5.3 5.3 ZrO.sub.2 4.6 4.6 4.6 2.6 3.1 4.6 4.6 Fe.sub.2O.sub.3 0.10
0.20 0.10 0.30 0.10 0.15 0.10 SnO.sub.2 -- -- 0.10 0.10 0.10 -- --
SO.sub.3 0.10 0.10 -- -- -- 0.05 0.10 Thermal expansion coefficient
83 83 82 83 84 81 82 [.times.10.sup.-7/.degree. C.] Density
[g/cm.sup.3] 2.82 2.83 2.83 2.76 2.79 2.81 2.82 Strain point
[.degree. C.] 626 626 625 616 613 630 630 Annealing point [.degree.
C.] 672 673 672 662 659 677 677 Softening point [.degree. C.] 867
870 881 863 855 875 878 10.sup.4 dPa s [.degree. C.] 1,159 1,164
1,186 1,164 1,154 1,165 1,174 10.sup.3 dPa s [.degree. C.] 1,309
1,317 1,342 1,321 1,311 1,314 1,326 10.sup.2.5 dPa s [.degree. C.]
1,409 1,418 1,444 1,424 1,416 1,411 1,425 Liquidus temperature
[.degree. C.] 1,104 1,098 1,126 1,112 1,109 1,121 1,098 Liquidus
viscosity log.sub.10.eta. 4.5 4.6 4.5 4.4 4.4 4.4 4.7 [dPa s]
Compression stress value 615 Not Not Not Not Not Not [MPa] measured
measured measured measured measured measured Stress layer depth
[.mu.m] 10 Not Not Not Not Not Not measured measured measured
measured measured measured Compression stress value [MPa] 570 Not
Not Not Not Not Not (after thermal treatment measured measured
measured measured measured measured at 540.degree. C. for 20
minutes) Stress layer depth [.mu.m] 10 Not Not Not Not Not Not
(after thermal treatment measured measured measured measured
measured measured at 540.degree. C. for 20 minutes) Thermal
shrinkage amount 60 Not Not Not Not Not Not (500.degree. C.) [ppm]
measured measured measured measured measured measured
TABLE-US-00003 TABLE 3 No. 15 No. 16 No. 17 No. 18 No. 19 No. 20
No. 21 Glass SiO.sub.2 51.0 51.0 50.7 51.0 51.0 51.0 51.0
composition Al.sub.2O.sub.3 13.0 13.0 13.0 12.0 13.0 13.0 12.0 (wt
%) B.sub.2O.sub.3 -- -- -- -- -- -- -- MgO 1.0 0.1 0.1 0.1 0.1 1.0
0.1 CaO 6.5 5.4 3.4 3.9 5.4 4.5 3.9 SrO 6.9 9.1 9.1 11.4 9.9 9.1
8.4 BaO 6.5 6.3 8.3 5.5 5.5 6.3 8.5 Li.sub.2O -- -- -- -- -- -- --
Na.sub.2O 5.0 5.0 5.0 5.5 5.5 5.0 5.5 K.sub.2O 5.3 5.3 5.3 4.8 4.8
5.3 4.8 ZrO.sub.2 4.6 4.6 4.6 5.6 4.6 4.6 5.6 Fe.sub.2O.sub.3 0.10
0.10 0.40 0.10 0.10 0.10 0.10 SnO.sub.2 -- -- -- -- -- -- --
SO.sub.3 0.10 0.10 0.10 0.10 0.10 0.10 0.10 Thermal expansion
coefficient 82 82 82 83 83 82 82 [.times.10.sup.-7/.degree. C.]
Density [g/cm.sup.3] 2.81 2.83 2.84 2.85 2.83 2.82 2.86 Strain
point [.degree. C] 629 630 628 628 628 626 625 Annealing point
[.degree. C.] 675 677 676 675 674 674 672 Softening point [.degree.
C.] 876 879 884 876 873 880 877 10.sup.4 dPa s [.degree. C.] 1,170
1,178 1,197 1,176 1,180 1,180 1,180 10.sup.3 dPa s [.degree. C.]
1,321 1,331 1,358 1,328 1,336 1,336 1,335 10.sup.2.5 dPa s
[.degree. C.] 1,419 1,431 1,464 1,428 1,439 1,438 1,437 Liquidus
temperature [.degree. C.] 1,135 1,096 1,106 1,076 1,096 1,098 1,071
Liquidus viscosity log.sub.10.eta. 4.3 4.7 4.8 4.9 4.7 4.7 5.0 [dPa
s] Compression stress value Not Not Not Not Not Not Not [MPa]
measured measured measured measured measured measured measured
Stress layer depth [.mu.m] Not Not Not Not Not Not Not measured
measured measured measured measured measured measured Compression
stress value [MPa] Not Not Not Not Not Not Not (after thermal
treatment measured measured measured measured measured measured
measured at 540.degree. C. for 20 minutes) Stress layer depth
[.mu.m] Not Not Not Not Not Not Not (after thermal treatment
measured measured measured measured measured measured measured at
540.degree. C. for 20 minutes) Thermal shrinkage amount Not Not Not
Not Not Not Not (500.degree. C.) [ppm] measured measured measured
measured measured measured measured
TABLE-US-00004 TABLE 4 No. 22 No. 23 No. 24 No. 25 No. 26 No. 27
No. 28 Glass SiO.sub.2 50.0 50.0 53.0 50.5 53.0 53.6 51.0
composition Al.sub.2O.sub.3 12.0 12.0 13.0 12.5 13.0 14.9 13.0 (wt
%) B.sub.2O.sub.3 -- -- -- -- -- -- -- MgO 0.1 0.1 0.1 0.1 1.1 1.0
0.1 CaO 3.9 3.9 5.4 3.9 7.7 7.8 6.5 SrO 8.4 8.4 9.1 8.4 9.1 9.1
11.8 BaO 9.5 8.5 6.3 8.5 3.0 3.0 2.5 Li.sub.2O -- -- -- -- -- -- --
Na.sub.2O 5.5 5.5 5.0 5.5 5.0 5.0 5.0 K.sub.2O 4.8 5.8 5.3 4.8 5.3
5.3 5.3 ZrO.sub.2 5.6 5.6 2.6 5.6 2.6 0.1 4.6 Fe.sub.2O.sub.3 0.10
0.10 0.10 0.10 0.10 0.10 0.10 SnO.sub.2 -- -- -- -- -- -- --
SO.sub.3 0.10 0.10 0.10 0.10 0.10 0.10 0.10 Thermal expansion
coefficient 83 85 82 82 83 84 83 [.times.10.sup.-7/.degree. C.]
Density [g/cm.sup.3] 2.88 2.86 2.78 2.86 2.75 2.71 2.81 Strain
point [.degree. C.] 624 620 614 629 620 614 637 Annealing point
[.degree. C.] 671 667 661 676 665 660 683 Softening point [.degree.
C.] 874 871 864 882 862 858 877 10.sup.4 dPa s [.degree. C.] 1,172
1,173 1,166 1,185 1,153 1,162 1,166 10.sup.3 dPa s [.degree. C.]
1,325 1,327 1,330 1,340 1,306 1,324 1,314 10.sup.2.5 dPa s
[.degree. C.] 1,425 1,427 1,436 1,441 1,406 1,431 1,412 Liquidus
temperature [.degree. C.] 1,079 1,077 1,114 1,140 1,151 1,153 1,145
Liquidus viscosity log.sub.10.eta. 4.8 4.8 4.4 4.4 4.0 4.1 4.2 [dPa
s] Compression stress value Not Not Not Not Not Not Not [MPa]
measured measured measured measured measured measured measured
Stress layer depth [.mu.m] Not Not Not Not Not Not Not measured
measured measured measured measured measured measured Compression
stress value [MPa] Not Not Not Not Not Not Not (after thermal
treatment measured measured measured measured measured measured
measured at 540.degree. C. for 20 minutes) Stress layer depth
[.mu.m] Not Not Not Not Not Not Not (after thermal treatment
measured measured measured measured measured measured measured at
540.degree. C. for 20 minutes) Thermal shrinkage amount Not Not Not
Not Not Not Not (500.degree. C.) [ppm] measured measured measured
measured measured measured measured
TABLE-US-00005 TABLE 5 No. 29 No. 30 No. 31 No. 32 No. 33 No. 34
Glass SiO.sub.2 53.5 51 49.1 50.1 50.6 58.1 composition
Al.sub.2O.sub.3 12.4 13.0 13.0 13.0 13.0 13.0 (wt %) B.sub.2O.sub.3
-- -- 1.9 0.9 0.4 -- MgO 0.1 0.1 0.1 0.1 0.1 2.0 CaO 5.1 5.4 5.4
5.4 5.4 2.0 SrO 11.2 11.9 11.9 11.9 11.9 -- BaO 3.3 3.5 3.5 3.5 3.5
-- Li.sub.2O -- -- -- -- -- 0.1 Na.sub.2O 5.7 6.0 6.0 6.0 6.0 14.5
K.sub.2O 4.1 4.3 4.3 4.3 4.3 5.5 ZrO.sub.2 4.4 4.6 4.6 4.6 4.6 4.5
Fe.sub.2O.sub.3 0.01 0.01 0.01 0.01 0.01 -- SnO.sub.2 0.19 0.19
0.19 0.19 0.19 0.3 SO.sub.3 -- -- -- -- -- -- Thermal expansion
coefficient 81 83 84 84 84 102 [.times.10.sup.-7/.degree. C.]
Density [g/cm.sup.3] 2.79 2.82 2.82 2.82 2.82 2.54 Strain point
[.degree. C.] 627 626 613 620 623 533 Annealing point [.degree. C.]
674 672 656 665 669 576 Softening point [.degree. C.] 875 867 839
854 861 793 10.sup.4 dPa s [.degree. C.] 1,176 1,159 1,121 1,141
1,151 1,142 10.sup.3 dPa s [.degree. C.] 1,333 1,309 1,269 1,290
1,300 1,319 10.sup.2.5 dPa s [.degree. C.] 1,437 1,409 1,486 1,511
1,523 1,431 Liquidus temperature [.degree. C.] 1,124 1,104 1,065
1,084 1,094 880 Liquidus viscosity log.sub.10.eta. 4.4 4.5 4.5 4.5
4.5 6.4 [dPa s] Compression stress value Not Not Not Not Not 890
[MPa] measured measured measured measured measured Stress layer
depth [.mu.m] Not Not Not Not Not 22 measured measured measured
measured measured Compression stress value [MPa] Not Not Not Not
Not -- (after thermal treatment measured measured measured measured
measured at 540.degree. C. for 20 minutes) Stress layer depth
[.mu.m] Not Not Not Not Not -- (after thermal treatment measured
measured measured measured measured at 540.degree. C. for 20
minutes) Thermal shrinkage amount Not Not Not Not Not 270
(500.degree. C.) [ppm] measured measured measured measured
measured
[0085] Each of the samples in the tables was produced as described
below. First, glass raw materials were blended so as to have glass
compositions shown in the tables, and melted at 1,580.degree. C.
for 8 hours using a platinum pot. Next, the resultant molten glass
was cast on a carbon plate and formed into a flat sheet shape. The
resultant glass was evaluated for its various characteristics.
[0086] The thermal expansion coefficient is a value obtained
through measurement of an average thermal expansion coefficient in
the temperature range of 30 to 380.degree. C. using a
dilatometer.
[0087] The density is a value obtained through measurement by the
well-known Archimedes method.
[0088] The strain point, the annealing point, and the softening
point are values obtained through measurement based on a method
described in ASTM C336.
[0089] The temperatures at viscosities at high temperature of
10.sup.4.0 dPas, 10.sup.3.0 dPas, and 10.sup.2.5 dPas are values
obtained through measurement by a platinum sphere pull up
method.
[0090] The liquidus temperature is a value obtained through
measurement of a temperature at which crystals of glass are
deposited after glass is pulverized and glass powder that passes
through a standard 30-mesh sieve (sieve opening: 500 .mu.m) and
remains on a 50-mesh sieve (sieve opening: 300 .mu.m) is placed in
a platinum boat and then kept for 24 hours in a gradient heating
furnace.
[0091] The liquidus viscosity is a value obtained through
measurement of a viscosity of glass at the liquidus temperature by
a platinum sphere pull up method.
[0092] Note that a non-tempered glass and a tempered glass have
different glass compositions microscopically in their surface
layers, but the glass compositions of the whole non-tempered glass
and whole tempered glass are not substantially different. Thus, the
values of characteristics such as thermal expansion coefficient,
density, and viscosity are not substantially different between the
non-tempered glass and tempered glass.
[0093] Both surfaces of Sample No. 8 were optically polished, and
ion exchange treatment was then performed. The ion exchange
treatment was performed by immersing each of the samples in a
KNO.sub.3 molten salt under the conditions of 460.degree. C. for 6
hours. Next, the surfaces of Sample No. 8 were washed. After that,
the number of interference fringes and each interval between the
interference fringes were observed with a surface stress meter
(manufactured by TOSHIBA CORPORATION, FSM-6000) to calculate the
compression stress value and thickness of the compression stress
layer. In the calculation, the refractive index of Sample No. 8 was
1.52, and the photoelastic constant thereof was 26 [(nm/cm)/MPa].
Further, Sample No. 8 to which the ion exchange treatment had been
applied was treated under the conditions of a temperature rise to
540.degree. C. at +5.degree. C./min, maintenance of the temperature
of 540.degree. C. for 20 minutes, and a temperature fall to room
temperature at -10.degree. C./min. After that, the stress
compression value and thickness of the compression stress layer
were calculated once again.
[0094] Both surfaces of Sample No. 34 were optically polished, and
ion exchange treatment was then performed. The ion exchange
treatment was performed by immersing each of the samples in a
KNO.sub.3 molten salt under the conditions of 420.degree. C. for 2
hours. Next, the surfaces of Sample No. 34 were washed. After that,
the number of interference fringes and each interval between the
interference fringes were observed with a surface stress meter
(manufactured by TOSHIBA CORPORATION, FSM-6000) to calculate the
compression stress value and thickness of the compression stress
layer. In the calculation, the refractive index of Sample No. 8 was
1.52, and the photoelastic constant thereof was 28 [(nm/cm)/MPa].
Further, Sample No. 34 to which the ion exchange treatment had been
applied was treated under the conditions of a temperature rise to
540.degree. C. at +5.degree. C./min, maintenance of the temperature
of 540.degree. C. for 20 minutes, and a temperature fall to room
temperature at -10.degree. C./min. After that, the stress
compression value and thickness of the compression stress layer
were calculated once again.
[0095] Next, glass materials were blended so that each of the glass
compositions according to Sample Nos. 8 and 34 was achieved, and
then the resultant glass batch was melted. After that, the
resultant molten glass was formed into a glass having a flat sheet
shape (a thickness of 0.7 mm) by a float method. In that case,
temperature setting was performed so that the temperature in the
vicinity of the inlet of a tin bath reached 1,200.degree. C. and
the temperature in the vicinity of the outlet thereof reached
around 700.degree. C. Subsequently, the glass was moved out from
the tin bath and was transported through an annealing furnace. In
that case, temperature setting was performed so that the
temperature in the vicinity of the inlet of the annealing furnace
reached about 700.degree. C. and the temperature in the vicinity of
the outlet thereof reached around 100.degree. C. Next, a glass
piece with a size of 30 mm in length, 160 mm in width, and 0.7 mm
in thickness was cut out from the resultant glass and was used as a
glass to be tempered. The thermal shrinkage amount (S) of the glass
to be tempered was measured in accordance with the following
procedure.
[0096] First, markings were vertically drawn at sites each located
20 to 40 mm inside from each edge of the strip-shaped sample piece
(glass to be tempered), and the sample piece was then folded and
divided horizontally. After the above-mentioned tempering treatment
was applied to only one of the divided sample pieces, the tempered
sample piece and the non-tempered sample piece were lined up,
followed by fixing of the both with an adhesive tape, and marking
shifts .DELTA.L.sub.1 and .DELTA.L.sub.2 were measured. In the
measurement, in the case where the positions of the markings of the
tempered sample piece were located inside the positions of the
markings of the non-tempered sample piece, .DELTA.L.sub.1 and
.DELTA.L.sub.2 were represented as positive values, and a volume
change amount S1 was calculated by using Equation 2 described
above. Subsequently, thermal treatment was applied only to the
tempered glass. The thermal treatment was carried out under the
conditions of a temperature rise to 500.degree. C. at +3.degree.
C./min, maintenance of the temperature of 500.degree. C. for 1
hour, and a temperature fall to room temperature at -3.degree.
C./min. After that, the thermally treated sample piece and the
non-thermally treated (and non-tempered) sample piece were lined
up, followed by fixing of the both with an adhesive tape, and
marking shifts .DELTA.L.sub.1 and .DELTA.L.sub.2 were measured. In
the measurement, in the case where the positions of the markings of
the thermally treated sample piece were located inside the
positions of the markings of the non-thermally treated sample
piece, .DELTA.L.sub.1 and .DELTA.L.sub.2 were represented as
positive values, and a volume change amount S2 was calculated by
using Equation 2 described below. Finally, the thermal shrinkage
amount of the glass to be tempered was calculated by using Equation
3.
[0097] As evident from Tables 1 to 5, each of Samples Nos. 1 to 33
has a strain point of 613.degree. C. or more, and hence it is
expected that, even if thermal treatment is applied at high
temperature, its compression stress is unlikely to disappear and
thermal shrinkage is unlikely to occur. Further, each of Samples
Nos. 1 to 33 has a temperature at a viscosity at high temperature
of 10.sup.2.5 dPas of 1,523.degree. C. or less, thus being
excellent in meltability. In addition, each of Samples Nos. 1 to 33
has a liquidus temperature of 1,153.degree. C. or less and a
liquidus viscosity of 10.sup.4.0 dPas or more, thus being excellent
in denitrification resistance.
[0098] On the other hand, Sample No. 34 had a high liquidus
viscosity but had a low strain point, and hence thermal treatment
under the conditions of 540.degree. C. for 20 minutes caused its
compression stress layer to disappear completely and Sample No. 34
had a thermal shrinkage amount of 270 ppm after thermal treatment
was performed under the conditions of 500.degree. C. for 1
hour.
INDUSTRIAL APPLICABILITY
[0099] As apparent from the foregoing description, the tempered
glass of the present invention is suitable for applications in
which a transparent conductive film having a high resolution, a
high transmittance, and a low electrical resistance is formed, the
applications including, for example, a cover glass for a touch
panel display, a substrate for a solar cell (in particular, a
substrate for a thin-film compound solar cell such as a CIS-based
solar cell), and a substrate for a dye-sensitized solar cell. In
addition, the tempered glass of the present invention is expected
to find use in applications requiring a high mechanical strength,
for example, a window glass, a substrate for a magnetic disk, a
substrate for a flat panel display, a cover glass for a solid image
pickup device, and tableware.
REFERENCE SIGNS LIST
[0100] 1 glass [0101] 1a non-tempered sample piece (non-thermally
treated sample piece) [0102] 1b tempered sample piece (thermally
treated sample piece) marking [0103] 2 marking
* * * * *